Project Summary/Abstract Only two new structural classes of antibiotics, exemplified by daptomycin and linezolid, have been introduced to the market in the past 50 years. This dearth of novel antibiotics is not due to lack of new chemical matter; indeed, dozens or even hundreds of molecules with antimicrobial activity are discovered annually, but the majority of these are not suitable for deployment as human therapeutics. Additionally, many of the antibiotics on the market have undesirable properties (e.g., toxicity, chemical instability, metabolic liabilities) that deter physicians from employing them. The high degree of structural complexity present in most of these molecules complicates medicinal chemistry efforts to improve their properties. Our laboratory seeks to address this challenge by developing modular strategies for the assembly of structurally complex classes of antibiotics that have not yet reached their potential as therapeutics. Unlike many total synthesis proposals, our primary goal is not to develop methods for the synthesis of natural products (although this can be accomplished with our approach), but rather to use their structural architectures to guide the development of new structural classes. During our first 2 years in operation, we have developed a modular, scalable synthesis of streptogramin antibiotics (J. Am. Chem. Soc. 2017, doi: 10.1021/jacs.7b08577), and we have made significant headway towards a practical synthesis of lankacidin antibiotics. With these preliminary results as groundwork, five years of NIGMS MIRA funding will enable the development structurally novel therapeutics based on these classes that have improved physicochemical properties, broader spectra of activity, and increased activity against multidrug-resistant strains of bacteria. This pursuit will be facilitated by chemical and biological innovations with broad applicability. We also propose a method for binding-induced hybridization of therapeutics that we believe will find use beyond the application to ribosome-targeting antibiotics. Our efforts will be enabled by strategic collaborations to enable crystallographic characterization of the binding interactions of our analogs (with Prof. Yury Polikanov, UIC) and to evaluate the efficacy of antibiotic candidates against a broad panel of bacterial pathogens, including many multi-drug resistant strains (with Dr. Dean Shinabarger, Micromyx). This research program is significant because it has the potential to expand the frontiers of chemical reactivity, to facilitate discoveries in structural biology, and to address an urgent unmet medical need.